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B.T.M. Watchmakers' Lathe
B.T.M. continued on Page 2

Literature is available for BTM Lathes

Other Lathes for watchmakers

Thought to have been first produced during WW2, when supplies of German machines by makers such as Lorch, G.Boley, Leinen and Wolf Jahn were unobtainable, the B.T.M. was a beautifully-made English watchmaker's lathe with a centre height of 50 mm and 165 mm available between centres - both the straight and gap beds some 254 mm long being available. However, the lathe must have been but a minor distraction for its makers, the British Tabulating Machine Company Limited, for this was a large organisation, long familiar with precision production methods, that may have made the machine to fulfil a Government contract.
B.T.M. were later to become ICT and then, in the 1970s, the well-known and very successful computer firm ICL. During the 1930s the company was based in Icknield Way, Letchworth in North Hertfordshire and licensed by the Tabulating Machine Company (TMC) of America (later IBM) to produce punched-card machines. However, in connection with the same products, they had also independently developed a particularly successful mechanism, the ingenious
Rolling-total Tabulator, a device that was to be further developed by B.T.M. (and adopted by IBM) and play an important part in scientific and commercial calculations during the 1940s and 1950s. Of even greater interest is that their background in complex machines gave B.T.M. the experience and skills necessary to undertake the development and manufacture of the 210 massive and ingenious mechanical "Bombe" mechanisms (known internally by the company as the 6/6502 or CANTAB) used at Bletchley Park from 1940 to 1945 as part of the programme to decoded enemy signals during World War Two. The "Bombe" was not a form of electronic computer, but an electromechanical device cleverly designed to rapidly "mirror" the operation of a German Enigma code machine.  The book "Hut Six" by Gordon Welchman (SBN 10: 0947712348  and ISBN 13: 9780947712341) gives a fascinating insight into the part played by the BTM Bombes in WW2
Continued below:

The complete B.T.M. outfit in its fitted wooden box as offered on the civilian market during the late 1940s

Continued:
Built along lines of the original light Swiss 'Geneva' pattern watchmakers' lathe - as distinct from the heavier American Webster Whitcombe (WW) models - the B.T.M. watchmakers' lathe had a round bed with the flat element at the top rather than at the (more usual) back. It was intended for, and widely used by, precision industries and the armed services for the manufacture and repair of mechanical instruments. It is unlikely that the lathes were built by B.T.M themselves, but rather designed and developed by them with manufacture farmed out to the Royal Ordnance, a Government organisation who have numerous factories dotted around the country side producing not only munitions but all kinds of high-precision mechanisms. The numbers built must have been considerable for the model continued to be available - in boxes marked "
Manufactured by ROF" (ROF referring to Royal Ordnance Factory) - in a black crackle finish until the early 1950s with sales handled by, amongst others, the well known machinery dealer E. H. Jones of Edgware Road, The Hyde, London N.W.9.
With a headstock that looks to have been an exact copy of that used on the 1920s and 1930s G.Boley watchmakers' lathe, the lathe had a maximum through-collet capacity of 4.8 mm (and partial of 5.4 mm), with the 8 mm bore headstock spindle running in plain bronze bearings with a stated running clearance of 0.00025". A spring-loaded pin was fitted as standard to engage in a ring of indexing holes in the front face of the headstock pulley. The lathe was always supplied in the maker's well-made lockable wooden box complete, unlike those from many competing makers, with lid-mounted, felt-padded holding blocks. A very generous level of equipment was included that enabled the lathe to be pressed into service immediately. Items included: a straight bed; a bed with a gap; compound screw-feed slide rest; headstock with hollow spindle and 3-step pulley; two tailstocks - one with a securing lug and one without; a  T-rest holder with wide and narrow Tees; box chuck; self-centring 3-jaw precision ring-scroll chuck; 5 step chucks (collets); a set of plain collets to take 1.5, 2.1, 3.2, 3.6, 4.0, 4.2, 4.4, 4.8, 5.2 and 5.4 mm diameters; a set of cone collets to take 0.8, 1.0, 1.2, 1.8, 2.4, 2.6 2.8 and 3.0 mm diameters; a driving chuck with carrier; a pulley runner for tailstock with two pulleys; two plain and six hollow centres, two carriers and a centre ejector with vulcanite knob and a driving belt. Available as extras were an electric motor and drive pulley, a round foot-stand for bench mounting and a lever-action tailstock.
One interesting aspect of the B.T.M. was the very robust, well-supported compound slide assembly that more closely resembled the design of those fitted to a precision instrument makers' lathe. It was carried on a large casting that formed a pseudo apron (though which the cross-feed screw carrier passed) and had an unusually long (split) hole through the base by which means it was clamped to the bed.
For the military market it is thought that the lathe was finished in dark green and for the civilian (apart from the crackle-black mounting post) in nickel plate or polished steel. According to reports by contemporary users, many of these lathes were returned from Reserve Stores after the war (together with masses of other unused, high-precision equipment) and sold off. However, they were not cheap and in 1946, in one of only two known public advertisements, were offered at £45 : 10s ; 0d for the fully-equipped version in a box and £26 : 4s : 6d for the basic model..

Main elements of the lathe; even a separate bed with a gap was supplied as part of the standard equipment. The motor looks ludicrously over-specified for the job - but would no doubt have lasted several lifetimes.

Optional Lever-action Tailstock

Standard bed, headstock and tailstocks with and without extension lugs.

Special bed with gap

Well-made fitted wooden box with, unlike those offered by many competing makers, a set of felt-covered retaining blocks in the lid.

Bracket to fit to bed carrying a flip-up T rest

Compound slide rest with circular tool clamp

B.T.M. continued on Page 2

Literature is available for BTM Lathes

email: tony@lathes.co.uk
Home   Machine Tool Archive   Machine-tools Sale & Wanted
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B.T.M. Watchmakers' Lathe

Other Lathes for watchmakers